Syrian government forces, backed by Russian airstrikes, have recaptured the historic city of Palmyra from Islamic State (IS) militants, an advance that President Bashar al-Assad hailed as an "important achievement" demonstrating the success of his army's fight against terrorism.

The loss of Palmyra is a major setback for the extremist IS group, which declared a caliphate in 2014 across large swaths of Syria and Iraq.

It follows a nearly three-week push by Assad's forces to recapture the central city, which IS militants overran in May 2015.

"The liberation of the historic city of Palmyra today is an important achievement and another indication of the success of the strategy pursued by the Syrian Army and its allies in the war against terrorism," Assad told a delegation of French parliamentarians in Damascus.

He also took a swipe at the global coalition striking Islamic State (IS) targets in Syria and Iraq, saying the Syrian Army's victory "shows the coalition -- led by the United States and including more than 60 countries -- isn't serious about fighting terrorism."

Syrian television announced earlier in the day that the army and its militia allies took complete control of Palmyra and were clearing mines and bombs set up by the militants.

The Syrian Observatory for Human Rights, a British-based monitoring group, said that there was still gunfire in the eastern part of the city early in the morning on March 27, but that the majority of IS militants there had pulled out and retreated east.

Retaking the town is a major symbolic and strategic victory for Assad's government, which has made steady gains in recent months against IS and opposition rebel groups.

PHOTO GALLERY: The Ancient City Of Palmyra

Ancient Palmyra Threatened By Islamic State Militants

The road linking Palmyra to Raqqa, an IS stronghold, is now under army control, which means that IS fighters can only retreat eastward toward the Iraqi border.

The Syrian Army's general command said that Palmyra would become "a launchpad to expand military operations" against IS forces in Raqqa and Deir al-Zor, another stronghold of the extremist group.

It vowed to "tighten the noose on the terrorist group and cut supply routes…ahead of their complete recapture."

Despite Russia's announcement that it was pulling out most of its military forces from Syria two weeks ago, Russian jets and helicopters carried out dozens of strikes over the ancient city at the height of the fighting.

The Russian Defense ministry said on March 27 that its forces had made 40 flights over the area of Palmyra during the last 24 hours, striking 117 targets and killing more than 80 militants, Russian news agencies reported.

The ministry added that the cease-fire in Syria had been violated 10 times during the past 24 hours but that overall it was holding, news agencies reported.

Kremlin spokesman Dmitry Peskov said President Vladimir Putin congratulated Assad on the recapture Palmyra in a March 27 phone call.

"In a conversation with the Syrian president, Vladimir Putin congratulated his colleague on Syrian forces liberating the city of Palmyra from terrorists, noting the importance of preserving this unique historic city for world culture," Russia's state-owned RIA Novosti news agency quoted Peskov as saying.

Meanwhile, Rami Abdulrahman, head of the British-based Observatory, said that 400 Islamic State fighters and 180 government troops and allied militiamen died in the fighting for Palmyra.

Abdulrahman described the battle as the single biggest defeat for the group since it declared an Islamic caliphate in the areas of Syria and Iraq that it controlled in 2014

IS fighters have been under pressure since Syrian and Iraqi military forces launched offensives to retake the key bastions in the group's self-proclaimed caliphate.

They were driven out of the Iraqi city of Ramadi only three months ago, a major victory for Iraq. They also lost the Iraqi city of Tikrit last year and the Syrian town of Al-Shadadi in February.

On March 24, the Iraqi Army announced that it would launch an offensive to retake Iraq's second-largest city, Mosul, which has been under IS control since June 2014.

Many of Palmyra's Roman-era relics, including the 2,000-year-old Temple of Bel and the iconic Arch of Triumph, have been blown up by IS, which claims they promoted "idolatry."

UNESCO has called the campaign of destruction a war crime punishable by the International Criminal Court.

Syrian television on March 27 broadcast footage from inside a Palmyra museum that showed toppled and damaged statues, as well as multiple smashed display cases.

The Syrian government's antiquities chief said other ancient landmarks remained standing and vowed to restore the damaged monuments.

"Palmyra has been liberated. This is the end of the destruction in Palmyra," Mamoun Abdelkarim was quoted by Reuters as saying. "How many times did we cry for Palmyra? How many times did we feel despair? But we did not lose hope."